An anatomical model of sensory extinction has been proposed which includes several principles: 1) injury to one sensory channel weakens its competitive position vis a vis a second sensory channel; 2) the extinction sign is directly related to the locus and extent of the lesion; and 3) a field may be extinguished by interruption of the callosal fibers from the relevant cortical sensory area to a specialized processing zone. These principles will be tested by determining: 1) the relationship between tactile extinction, sensory deficits and impaired reaction time; 2) the association between extinction in the tactile, auditory, and visual modalities on the one hand and lesions in the respective cortical sensory areas on the other; and 3) the reversibility of extinction in the verbal test mode by an extinction test in the nonverbal mode, or vice versa. In addition, we will compare the effectiveness of first-order with second-order lesions in the production of extinction. Further, the distribution of the sensory representations in the callosum will be examined under extinction conditions. Extinction tests in the three modalities, in both the verbal and nonverbal form, will be administered to relatively nonselected patients. Lesion extent and locus will be determined by CT scan and angiography.